This invention relates to a process for producing silicon nitride bodies of near theoretical density. More particularly, it provides a silicon nitride composition from which bodies of near theoretical density can be produced by cold pressing and sintering.
In general, silicon nitride by itself has limited usage. In order to produce materials for turbines, cutting tools, wear parts, and the like, composites are needed which can be pressed to near theoretical density, that is, greater than about 96% of the theoretical density. U.S. Pat. Nos. 3,950,464 and 3,953,221 cite compositions of silicon nitride and sintering aids such as yttria and alumina to aid in densification. However, with the use of yttria the material cannot be cold pressed and sintered to the desired near theoretical density.
The process of this invention involves use of silicon nitride with lanthanum or lanthanum-aluminum compounds which can be cold pressed and sintered to near theoretical density.